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Hydrological modelling of drained blanket peatland

Ballard, C.E., McIntyre, N., Wheater, H.S., Holden, J., Wallage, Z.E.
Journal of hydrology 2011 v.407 no.1-4 pp. 81-93
drainage, floods, highlands, hydrologic models, issues and policy, land management, model uncertainty, model validation, peat, peatlands, prediction, surface roughness, water flow, water quality, water table, United Kingdom
Open ditch drainage is a commonly implemented land management practice in upland blanket peatlands, particularly in the UK, where policy decisions between the 1940s and 1970s led to widespread drainage of the uplands. The change in the hydrological regime associated with the drainage of blanket peat is poorly understood, yet has perceived importance for flooding, low flows and water quality. We propose a new simplified physics-based model that allows the associated hydrological processes and flow responses to be explored. The model couples four one-dimensional models to represent a three-dimensional hillslope, allowing for the exploration of flow and water table response throughout the model domain for a range of drainage configurations and peat properties. The model is tested against a data set collected from Oughtershaw Beck, UK, with results showing good model performance for wet periods although less conformity with borehole observations during rewetting periods. A wider exploration of model behaviour indicates that the model is consistent with the hydrological response reported in the literature for a number of drained blanket peat sites, and therefore has potential to provide guidance to decision makers concerning the effects of management practices. Through a global sensitivity analysis, we conclude that further field investigations to assist in the surface and drain roughness parameterisation would help reduce the uncertainty in the model predictions.